GeTec Ingenieurgesellschaft für Informations- und Planungstechnologie mbh. Überreicht durch

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1 Supporting measures for urban tunnelling Dipl.-Ing. Paul Thurlow GeTec UK Dipl.-Ing. Henry Knitsch GeTec Ingenieurgesellschaft, Offenbach Überreicht durch GeTec Ingenieurgesellschaft für Informations- und Planungstechnologie mbh Aachen Office D Aachen, Rotter Bruch 26a Fax Rhein-Main Office Fax th International Symposium on Field Measurements in GeoMechanics Berlin, September 12-16,2011 Publication GT E

2 Supporting measures for urban tunnelling Paul THURLOW, Getec UK Henry KNITSCH, GeTec De Introduction The improvement of urban infrastructure, particularly the building of efficient and attractive links for public commuter transportation, can often only be achieved by means of tunnels, in view of the amount of space available overground. The following paper shows how intelligent use of software linked with compensation grouting and geotechnical instrumentation provides the stakeholders with confidence to proceed with complicated underground construction activities in an urban environment using the principles of the observation method. Methods Sensitive buildings are frequently located within the zone of influence of tunnels and spray concrete lined caverns, which have to be monitored for movement during the tunnel construction. This is usually because of Stakeholders commitments to the public or sensitive structures identified during structural surveys. The interactions between the existing building, subsurface construction processes and groundwater are extremely complex. Definitive methods of measuring and reporting in a clear and precise manner are now a standard within the Instrumentation and Monitoring industry. As a result, intelligent, adaptive supporting and compensation measures in keeping with the observation method principle are all the more important. Process-integrated supporting measures. Process integrated supporting measures are designed to prevent damage occurring to buildings or to compensate for removal of materials at depth during tunnel construction. The examples in this paper relate to compensation grouting and TBM control measures. Controlling variables must be undertaken based on measured values, which have to be collated with a continuous process control from a real time measurement system and evaluated and visualised. Real time measurement systems can be accomplished nowadays with a multitude of sensors reporting data in real and near real time. This enables the end users to be well informed of the construction process and to be able to plan, control and efficiently manage the works with confidence. The major items of instrumentation in use on large urban tunneling projects consist of the following; Hydrostatic Water Level Systems, system GeTec (settlement) Automatic Total Stations (settlement and tilt) Precise level monitoring (settlement) Inclinometers (tilt) Displacement transducers (crack and Sewer monitoring) 1

3 Strain transducers (structural stresses) Load cells and pressure pads (stresses in SCL lining) Piezometer (pore water pressures) Extensometers (subsurface compression and elongation) Horizontal and vertical inclinometers (transversal movements) Shape array (movement and vibrations) Figure 1:Different sensors in multi channel measurement systems. Extensometer, Rod extensometer,strain gauge,piezometer,pressure cells and Hydrostatic level cells. (images courtesy of RST instruments). To enable engineering interpretation of the interactions between the construction and the measured values from the site, the data must be stored, evaluated and visualised with a suitable software system. For mechanised tunnel drives GroutControl Software [10, 12, 13, 14] is one such available programme. It represents a database application, which was devised by the GeTec Ingenieurgesellschaft mbh from many years working in the mining industry and was adopted primarily to be used for compensation grouting projects. The system is linked to a database via an open interface (various data systems can be used), in which the measured values of the real time measurement systems (e.g. liquid level gauge [4, 5, 6]), measurement values from geodetic systems (total station, levelling unit) as well as the essential driving parameters are stored. 2

4 Figure 2: Overview of data flow on site using various geotechnical instruments All stored values are continuously evaluated and displayed in various presentations and process images. The ability to playback data in an archive mode, which can include the various visualistion modes such as contouring, volume loss and positions of excavated tunnel face variables along with all measurement values allows for a data presentation in a more efficient manner. The spectrum ranges from the complete overview of the tunnel drive by way of the presentation of the current extract for the shield operator right up to detailed presentations and time variation plots for individual measurement values. Visulisation in the form of maps, images and graphs can be provided, which facilitate orientation within the project and the allocation of measured and controlled variables to sensors or affected buildings. For visualisation purposes an automatic 3D-CAD core is used. This CAD core permits a 3D underground model for the entire project to be set up, in which the geological and hydrogeological conditions can be taken into account alongside the geometry. The position of the TBM is shown real time in position on the GIS system. The software can select influence zones that reflect the forwarding and rear monitoring zones and assign these as priority readings to provide a clear understanding of settlement influences. The volume loss calculation is shown automatically from the assigned points.the data from the TBM can be managed to reflect the requirements in shield pressure and back pressure grouting, as well as groundwater levels. The TBM operator has a module that provides the TBM data in a visual format for the required parameters against the measured. It also features the monitoring in- 3

5 formation at surface and sub surface, with the same interaction as users. The influence of the TBM and monitoring data is dynamic and real time. This enables the TBM engineers to assess the whole sphere of works immediately. Figure 3: TBM operators view of surface data alongside permitted sheild pressures to suit conditions. GroutControl development as a client-server system enables a number of users to obtain the data at the same time. It is possible to award different access rights. On this basis different presentations and formatted reports can be defined. The construction management, client, tunnel team and other stakeholders obtain their individually configurated site layouts with the data and information relevant for them. When assessing the overall situation a multistage comparison of all measured and control variables is possible with previously determined limit values in the form of a traffic light control system. The trigger levels and the alarms assigned to the individual measurement points are user defined, with various layers of control. The alarm system also responds to these predetermined limit values, which provides automatic reports via SMS and to a freely configurable alarm chain. As a result of this automatic alarm system the operating safety of the entire system is considerably enhanced 4

6 Figure 4. Graphical representation of data from GroutControl 5

7 Autonomous supporting measure Should a suitable control variable be lacking in the selected TBM driving technology or large underground caverns are to be constructed using SCL methods, then the use of other supporting measures to complement these processes is recommended. Compensation grouting is classed as an autonomous supporting measure. The controlled variables for compensation grouting to attain movements or heave in the ground are: grout volume and grouting pressure. These main parameters as well as others are controlled in precise ways using advanced technology. Compensation grouting within an urban area requires a high degree of control. The integration of grouting information and instrumentation is a key factor to successful grouting works and reducing site risk. In areas that require the control of compensation or jet grouting the information is overlain so that the underlying monitoring & TBM data is unchanged and continually monitoring the project.in the specific areas of compensation grouting, the positions of the boreholes are inputted into the programme after being measured by a specialist orientation device. This then calculates numbers and positions the tam locations in relation to the tunnel alignment and structures. The grouting data derived from the pump container is stored and represented real-time, alongside the monitoring data. The grouting process is controlled by the volume and pressure injected into the ground and the structural response to that injection. The grouting engineers are able to dynamically assess the structural response to injections, working within predetermined parameters which can be assigned to grouting phases, and individual tam locations. The instructions can also be written in GroutControl and use parameters such as volume, pressure & heave. All limits and alarms, whether grout or instrumentation can be quickly assigned by the registered user. 6

8 Figure 5. Configuration of compensation grouting boreholes and TaM locations Once the TaM pipes have been installed, a phase of pre- treatment is carried out. This involves injecting grout at set areas to effectively heave the ground to compensate for settlement during the TaM installation and to heave the ground ahead of excavation works: the specified heave allowance is usually 5mm. During the process of pre-treatment, it is important that the reaction of structures to the grouting is accurately identified. Through the compacting effect on the soil lying between the hardening layers of solid material and through the solid material itself the soil s mechanical properties (strength, stiffness and consistency) are improved. During the tunnelling and SCL works, the grouting works will require careful planning due to the various exclusion zones. The GroutControl software will assist in providing a visual and computed reference to these areas. Effective communication between tunnelling, grouting and monitoring teams is vital. The realtime feedback to the monitoring software and dynamic review from the grouting engineers is the key factor in establishing a controlled approach to grouting, monitoring, construction safety and progress. Specification limits are set on slope and deflection ratio, together with related trigger values. Control values are usually set on settlement associated with each individual construction activity. 7

9 Figure 6. 3 D display of cumulative grouting volume. Summary Efficient systems are available for face supporting during tunnel construction and compensation measures in areas where there are more complicated subsurface works. These systems permit a precise analysis on the effects of buildings influenced by the tunnel or excavation in real time through systematic storage, evaluation and engineering presentation of measurement values and controlled variables The safety and risk reduction of a tunnel drive and the support of associated auxiliary structures has increased significantly through the application of these intelligent and adaptable control mechanisms. 8

10 References [1] Kramer, G. J. E.; Tavares, P. D.; and Droof, E. R. (1994): Settlement Protection Workfor the New St. Clair River Rail Tunnel, Proceedings of Canadian Tunneling, BiTech Publisher, Richmond, BC, Canada, pp [2] H. Knitsch: Rückstellungen von Setzungen mit IT-gestütztem Soil-frac - Verfahren, Vortrag Fachtagung EDV in der Baupraxis 2000, Spittal a. d. Drau, Austria. [3] Säuberlich, J. R.; Knitsch, H.; Ruppel, G.; Trunk, U.: Rückstellungen von Setzungen mit dem Soilfrac -Verfahren: Zusammenspiel von Messen, Injektion und geotechnischem Modell an einem Beispiel, Messen in der Geotechnik 2000, TU Braunschweig. [4] Jakobs, M.; Knitsch, H.; Wieland, R.: Ein Druckschlauchwaagensystem für die kontinuierliche Deformationsüberwachung und die Steuerung des Soilfrac -Verfahrens während der Untertunnelung der Centraalstation Antwerpen, Messen in der Geotechnik 2002, TU Braunschweig. [5] Chambosse, G.; Otterbein, R.: State of the art of Compensation Grouting in Germany International Conference on soil mechanics and Geotechnical Engineering, 2001, Istanbul. [6] Jakobs, M.; Otterbein, R.; Dekker, H.: Erfahrungen beim Einsatz der Druckschlauchwaage zur Höhenüberwachung setzungsempfindlicher Bauwerke, Veröffentlichung Bauingenieur Band 76, [7] Franz, S.; Kirsch, F.; Richter, T.: Der City Tunnel Leipzig Umfängliche Gebäudesicherungen durch Hebungsinjektionen, Vorträge zum 2. Hans Lorenz Symposium, Veröffentlichungen des Grundbauinstituts TU Berlin, S , [8] Knitsch, H.; Otterbein, R.; Paßlick, T.: Visualisierung relevanter Daten beim Compensation Grouting, Vortrag anlässlich des BHT 2007, TU Bergakademie Freiberg. [9] Knitsch, H.; Wieland, R.; Pandrea, P.: Datenmanagement und Datamining als Anwendungsvoraussetzung für Verfahren des Spezialtiefbau, Messen in der Geotechnik 2008, TU Braunschweig. [10] Jakobs, M.; Siebers, F.; Vorthmann, F.: Kontinuierliche vortriebsbegleitende Deformations-überwachung der Inntalautobahn A12 und der Eisenbahnstrecke Innsbruck Kufstein während der Auffahrung des Tunnel Jenbach, Messen in der Geotechnik 2008, TU Braunschweig [11] Kirsch, F. ; Trunk, U.; und Richter, T.: Das Verfahren des Compensation Grouting beim Bauvorhaben CityTunnel Leipzig: Hebungsinjektion oder Baugrundverbesserung, Vorträge der Baugrundtagung 2008 in Dortmund, S , DGGT [12] Assenmacher, S.; Gabener, G.; Hicking, W.; Oligmüller, L.: Optimale Steuerung von Schildvortrieben mit Hilfe von ATDS, Veröffentlichungen des Grundbauinstitutes der Technischen Universität Berlin Heft Nr. 42, Berlin 2008 [13] Knitsch, H.: Visualization of Relevant Data for Compensation Grouting, Tunnel 3/2008, Page [14] Knitsch, H.: Steering Supporting Measures for Urban Tunnelling, Tunnel 2/2010, Page [15] DIN EN 12715: Ausführung von besonderen geotechnischen Arbeiten: Injektionen. 9